X-ray tubes may be used in a variety of applications to scan and reconstruct one or more images of an object. For example, in computed tomography (CT) imaging systems an X-ray tube may be part of an X-ray source that emits a fan or cone shaped beam toward an object. A typical object may include a patient, a patient's body part, a package, a piece of baggage, a manufactured component, or other object to be scanned. The X-ray beam is attenuated by the object and impinges upon a detector array. Each detector element of the detector array produces an electrical signal indicative of the attenuated beam received by the individual detector element. The electrical signals are transmitted to a data processing system for generating images of the object and for additional analysis.
In some computed tomography imaging systems, the X-ray source and the detector array are rotated about a gantry around the object. The detector array may include a collimator for collimating X-ray beams received at the detector, a scintillator disposed adjacent to the collimator for converting X-rays to light energy, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals.
FIG. 1 shows a diagram of an X-ray tube assembly 100. The X-ray tube assembly 100 may include a filament or emitter 120 and an anode 116. The filament or emitter 120 produces an electron beam 102 that impinges on anode 116 to produce an X-ray beam 180.
The filament or emitter 120 may be part of a cathode assembly 110, including cathode assembly shield 114 enclosing the filament or emitter 120, and a series of electrodes including a focusing electrode 130, an extraction electrode 140, and a downstream focusing electrode 150. The filament or emitter 120 may be heated, for example, by passing a relatively large current through the filament or emitter 120. A voltage source 124 may supply this current to the filament or emitter. A potential difference may be applied between the cathode assembly 110 and anode 116, otherwise known as a target, to accelerate the electron beam 102 from the filament or emitter 120 toward the anode 116. An exemplary potential difference within a range from about 40 kV to about 450 kV may be applied using a high voltage feedthrough 126 to set up a potential difference between the cathode assembly 110 and the anode 116.
In some embodiments, one or more portions of each of the electrodes 130, 140, 150 may be maintained at static or variable voltage potentials in order to focus the electron beam 102. A flow of electrons in the electron beam 102 from the filament or emitter 120 toward the anode 116 may be controlled by altering the voltage potential of one or more portions of the electrodes 130, 140, 150. In some embodiments, the size (e.g., width, diameter, cross-sectional area) and the intensity of the electron beam 102 may also be controlled by altering the voltage potential of one or more portions of the electrodes 130, 140, 150.
The X-ray tube 100 also includes a magnetic assembly 160 for focusing or positioning and deflecting the electron beam 102 on the anode 116. The magnetic assembly 160 may be generally disposed between the cathode assembly 110 and the anode 116. The magnetic assembly 160 generally includes magnets 162 for influencing focusing and or deflection of the electron beam 102 by creating a magnetic field that shapes and or deflects the electron beam 102 on the anode 116. The magnets 162 may include a cathode side quadrupole 162A and an anode side quadrupole 162B.
FIG. 2 shows an isometric illustration of the cathode side quadrupole 162A and the anode side quadrupole 162B. The cathode side quadrupole 162A has a core 200 with members 202, 204 extending along the Y-axis, and members 206, 208 extending along the X-axis, referred to as cross bars. Cross bars 206, 208 may each be separated by a gap 210, 212, respectively. The cathode side quadrupole 162A includes a plurality of poles with pole windings, referred to as QC windings 214, 216, 218, 220 connected in series. The polarities of the QC windings are arranged so that electrons are pushed into the YZ plane.
The target side quadrupole 162B similarly has a core 230 with members 232, 234 extending along the Y-axis, and members 236, 238 extending along the X-axis, also referred to as cross bars. Cross bars 236, 238 may each be separated by a gap 240, 242, respectively. The anode side quadrupole 162B includes a plurality of poles with pole windings, referred to as QT windings 244, 246, 248, 250 connected in series. The polarities of the QT windings are arranged such that electrons are pushed into the ZX plane. The anode side quadrupole 162B also has pole windings, also referred to as DY windings 252, 254, 256, 258 wound with the QT windings 244, 246, 248, 250 and independently connected in series. In addition, the anode side quadrupole 162B has windings mounted on the core, referred to as DX windings 260, 262 independently connected in series.
The QC windings 214, 216, 218, 220, and QT windings 244, 246, 248, 250 are used to focus the electron beam 102 (FIG. 1) and affect the focal spot size and shape. The DY windings 252, 254, 256, 258 and the DX windings 260, 262 are used for focal spot alignment and or deflection with the DY windings deflecting the focal spot in the +/−Y direction and the DX windings deflecting the focal spot in the +/−X direction.
The quadrupole configuration provides very precise control of the electron beam with relatively fast reaction times. As a result, X-ray tubes are increasingly becoming reliant on magnetic control of the x-ray producing electron beam for focusing and deflection. In addition, a higher density electron beam in the X-ray tube is advantageous for higher resolution images. Furthermore, computed tomography systems are running at higher gantry rotational speeds for more rapid image capture. There is a need for magnetic focusing and deflection systems that may accommodate a higher density electron beam and that require less material, less mass, and less power.